Gas turbine engines are sometimes used to power driven equipment. For example, gas turbine engines are sometimes used to power centrifugal compressors used in the oil and gas industry. In particular, the gas turbine engines are used to power centrifugal compressors used to transport fluids such as, for example, natural gas. Since demand for the fluids fluctuates, the gas turbine engines are not always sized to efficiently power the centrifugal compressors. For example, gas turbine engines that are sized to power the centrifugal compressors during peak demand periods are not sized to efficiently power the centrifugal compressors during low demand periods. Unfortunately, this leads to excessive fuel costs and emissions during low demand periods.
One way to reduce fuel costs is disclosed in U.S. Pat. No. 5,689,141 (the '141 patent) issued to Kikkawa et al. on Nov. 18, 1997. The '141 patent discloses a compressor drive system for a natural gas liquefaction plant. The compressor drive system includes a plurality of gas turbines. Additionally, the compressor drive system includes an electric motor associated with each of the gas turbines. Each electric motor serves both as an auxiliary electric motor for generating a startup torque and as an AC generator. When the power requirement of a compressor associated with one of the gas turbines is less than the power output of the gas turbine, the electric motor converts the excess output power of the gas turbine into electric power. This allows the gas turbine to operate efficiently, resulting in reduced operating costs through fuel savings.